1. Field of the Invention
This invention pertains to construction of lightweight, leakproof, and moisture-proof packaging enclosures for various electrochemical devices, such as lithium-ion-polymer batteries, ultracapacitors and other kinds of batteries and devices, in which said enclosures, have hard metal walls joined and sealed by heat welding of plastic layers attached to them. This invention also describes the method of assembly of said enclosures.
2. Description of the Prior Art
Prior art lithium polymer prismatic cells are usually heat sealed in a soft and thin aluminum, plastic coated foil pouches or bags, which may be later inserted into a hard box to create a multi-celled battery with the cells in series, as described in the U.S. Pat. No. 5,057,385 (claim 1), and U.S. Pat. No. 5,350,647 of Hope at al. The polymer cells do not require hard casings to hold them together because they are laminated, (welded or glued). The aluminum foil protects the cells from moisture, and the plastic layer is used for heat weld seal. Major problem is with the sealing of the cell terminals existing from the pouch, due to the steps in the thickness of the seal, caused by the flat foil terminals presence. The plastic layers during welding do not always flow into the gaps created by the terminals, which creates openings and leaks of the electrolyte, or a moisture entry into the pouch, and thus spoilage of the cell. The aluminum pouch is also a poor protector of the cell, since it can be easily punched through by a sharp object, also bends easily or cracks at the corners when the seal is folded, which again creates leaks and/or spoilage of the cell. Sometimes the terminals during the seal welding cut through the plastic layer and touch the aluminum foil, which causes electronic shorts and damage to the cells and thus a low production yield.
The prismatic, liquid electrolyte lithium based cells, nickel metal hydride cells, or prismatic capacitors, ultracapacitors or other electrochemical devices are usually inserted into a rectangular hard metal vessel having a metal lid with insulated terminals welded to the vessel which seals the devices therein. The hard casing is necessary to hold the cells or devices tightly together, and to create a pressure on the stack of the cells for proper functioning.
The described prior art hard casings are expensive, heavy, slow to weld, and have size limitations, due to the limited stiffness of the casings and their ability to maintain pressure on the stack. The heavy casings decrease the energy density of the devices.
Prismatic packaging structure for electrochemical devices of this invention does not suffer from prior art problems and provides superior cell protection, energy density improvements, reduced cost, and many other positive advantages.